The present invention relates to an air introduction system, and more particularly to an active noise control microphone which is hardened against a hostile environment.
Manufacturers have employed active and passive methods to reduce engine noise within the passenger compartment. Such noise frequently emanates from the engine, travels through the air induction system and emanates into the passenger compartment.
Active systems use a speaker to create a canceling sound that attenuates engine noise. The sound created is out of phase with the engine noise and combines with this noise to result in its reduction. Generally, this sound is generated in proximity to the inlet of the air induction system. In one such system, a control unit, such as a digital signal processor, obtains data from the vehicle engine, creates a predictive model of engine noise, and thereby generates the appropriate cancellation signal based on the results of this model. This signal is then transmitted to the speaker, which transforms the signal into a canceling sound. Because the control unit may not perfectly model engine noise, an error microphone is placed in proximity to the intake of the air induction system to determine if engine noise need be further attenuated.
Typically, the error microphone and speaker are mounted to the air induction system. During vehicle operation the microphone may be subject to damage caused by weathering including snow, mud, ice, stones, leaves insects, and other environmental conditions. To move the microphone may cause the noise attenuation system to function less than optimally.
Accordingly, it is desirable to provide a mounting arrangement for an active noise control microphone which hardens the microphone against environmental conditions.
The air introduction system according to the present invention provides an active noise control system which includes an environmentally protected microphone. A support structure defines a louvered cage over a microphone reception cavity. The microphone is mounted to a circuit board which fits within the microphone reception cavity. The louvered cage is formed by the support structure to protect the microphone from relatively large debris such as rocks and the like. A cover fits into the cavity opposite the louvered cage to encase the microphone therein. A seal such as an O-ring assures the cover waterproofs the cavity.
An open cell foam surrounds the microphone and a waterproof material encases the foam. The waterproof material encases the foam with an excess amount of material such that waterproof material provides for internal air expansion and contraction. Applicant has determined that by locating the foam between the microphone and the waterproof material improved transmission of acoustic waves is provided which thereby maintains microphone sensitivity.
The present invention therefore provides a mounting arrangement for an active noise control microphone which hardens the microphone against environmental conditions.